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Configuration Guide - Device Management

CloudEngine 12800 and 12800E V200R005C10

This document describes the configurations of Device Management, including device status query, hardware management, Information Center Configuration, NTP, Synchronous Ethernet Configuration, Fault Management Configuration, Energy-Saving Management Configuration, Performance Management Configuration, Maintenance Assistant Configuration, and OPS Configuration.
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Huawei uses machine translation combined with human proofreading to translate this document to different languages in order to help you better understand the content of this document. Note: Even the most advanced machine translation cannot match the quality of professional translators. Huawei shall not bear any responsibility for translation accuracy and it is recommended that you refer to the English document (a link for which has been provided).
NTP Operating Mode

NTP Operating Mode

A device may use one of the following NTP operating modes to perform time synchronization. You can select an appropriate operating mode as required.

Unicast Server/Client Mode

The unicast server/client mode runs on a higher stratum on a synchronous subnet. In this mode, devices need to obtain the IP address of the server in advance.

  • Client: A host running in client mode (client for short) periodically sends packets to the server. The Mode field in the packets is set to 3, indicating that the packets are coming from a client. After receiving a reply packet, the client filters and selects clock signals, and synchronizes its clock with the server that provides the optimal clock. A client does not check the reachability and stratum of the server. Usually, a host running in this mode is a workstation on a network. It synchronizes its clock with the clock of a server without changing the clock of the server.

  • Server: A host running in server mode (server for short) receives the packets from clients and responds to the packets received. The Mode field in reply packets is set to 4, indicating that the packets are coming from a server. Usually, the host running in server mode is a clock server on a network. It provides synchronization information for clients without changing its own clock.

Figure 4-3 Unicast Client/Server Mode

During and after the restart, the host operating in client mode periodically sends NTP request messages to the host operating in server mode. After receiving the NTP request message, the server swaps the position of destination IP address and source IP address, and the source port number and destination port number, fills in the necessary information, and sends the message to the client. The server does not need to retain state information. The client adjusts the interval for sending NTP request messages according to the local conditions.

Peer Mode

The peer mode runs on a lower stratum on a synchronous subnet. In this mode, an active peer and a passive peer can synchronize with each other. The peer with a higher stratum (a lower level) synchronizes with a peer with a lower stratum (a higher level).

In peer mode, the active peer sends an NTP packet with the Mode field set to 3 (the client mode), and the passive peer responds with an NTP packet with the Mode field set to 4 (the server mode). This interaction creates a network delay so that devices at both ends enter the peer mode. The following describes the two peer types:

  • Active peer: A host that functions as an active peer sends packets periodically. The value of the Mode field in a packet is set to 1. This indicates that the packet is sent by an active peer, without considering whether its peer is reachable and which stratum its peer is on. The active peer can provide time information about the local clock for its peer, or synchronize the time information about the local clock based on that of the peer clock.

  • Passive peer: A host that functions as a passive peer receives packets from the active peer and sends reply packets. The value of the Mode field in a reply packet is set to 2. This indicates that the packer is sent by a passive peer. The passive peer can provide time information about the local clock for its peer, or synchronize the time information about the local clock based on that of the peer clock.

Figure 4-4 Peer mode

NOTE:

The passive peer does not need to be configured. A host sets up a connection and sets relevant state variables only when it receives an NTP packet.

Broadcast Mode

The broadcast mode is applied to the high speed network that has multiple workstations and does not require high accuracy. In a typical scenario, one or more clock servers on the network periodically send broadcast packets to the workstations. The delay of packet transmission in a LAN is several milliseconds.

  • Broadcast server: A host that runs in broadcast mode periodically sends clock synchronization packets to the broadcast address 255.255.255.255. The value of the Mode field in a packet is set to 5. This indicates that the packet is sent by a host that runs in broadcast or multicast mode, without considering whether its peer is reachable and which stratum its peer is on. The host running in broadcast mode is usually a clock server running high-speed broadcast media on the network, which provides synchronization information for all of its peers without altering its own clock.

  • Broadcast client: The client listens to the clock synchronization packets sent from the server. When the client receives the first clock synchronization packet, the client and server exchange NTP packets whose values of Mode fields are 3 (sent by the client) and the NTP packets whose values of Mode fields are 4 (sent by the server). In this process, the client enables the server/client mode for a short time to exchange information with the remote server. This allows the client to obtain the network delay between the client and the server. Then, the client returns the broadcast mode, and continues to sense the incoming clock synchronization packets to synchronize the local clock.

Figure 4-5 Broadcast mode

Multicast Mode

Multicast mode is useful when there are large numbers of clients distributed in a network. This normally results in large number of NTP packets in the network. In the multicast mode, a single NTP multicast packet can potentially reach all the clients on the network and reduce the control traffic on the network.

  • Multicast server: A server running in multicast mode periodically sends clock synchronization packets to a multicast address. The value of the Mode field in a packet is set to 5. This indicates that the packet is sent by a host that runs in broadcast or multicast mode. The host running in multicast mode is usually a clock server running high-speed broadcast media on the network, which provides synchronization information for all of its peers without altering its own clock.

  • Multicast client: The client listens to the multicast packets from the server. When the client receives the first broadcast packet, the client and server exchange NTP packets whose values of Mode fields are 3 (sent by the client) and the NTP packets whose values of Mode fields are 4 (sent by the server). In this process, the client enables the server/client mode for a short time to exchange information with the remote server. This allows the client to obtain the network delay between the client and the server. Then, the client returns the multicast mode, and continues to sense the incoming multicast packets to synchronize the local clock.

Figure 4-6 Multicast mode

Manycast Mode

Manycast mode is applied to a small set of servers scattered over the network. Clients can discover and synchronize to the closest manycast server. Manycast is especially applicable when the identity of the server is not fixed and a change of server does not require reconfiguration of all the clients in the network.

  • Manycast client: The client in manycast mode periodically sends request packets (with the Mode field is set to 3) to an IPv4/IPv6 multicast address. After receiving a reply packet, the client filters and selects clock signals, and synchronizes its clock with the server that provides the optimal clock.

  • Manycast server: The manycast server continuously listens to the packets. If a server can be synchronized, the server returns a packet (with the Mode field is set to 4) by using the unicast address of the client as the destination address.

To prevent the client from constantly sending NTP request packets to the manycast server and reduce the load on the server, the NTP protocol defines a minimum number of connections. In manycast mode, the client records the number of connections established every time it synchronizes the clock with the server. The minimum number of connections is the minimum number of connections called during a synchronization process. If the number of connections called by the client reaches the minimum number during subsequent synchronization processes and the synchronization is completed, the client considers that the synchronization is completed. After that, the client sends a packet every time a timeout period expires to maintain the connection. The NTP protocol uses the time to live (TTL) mechanism to ensure that the client can successfully synchronize with the server. Every time the client sends an NTP packet, the TTL of the packet increases (starting from the initial value of 1) until the minimum number of connections is reached or the TTL value reaches the upper limit. If the TTL reaches the upper limit or the number of connections called by the client reaches the minimum number, but connections called by the client still cannot complete the synchronizing process, the client stops data transmission in a timeout period to eliminate all connections. Then the client repeats the preceding process.

NOTE:

In NTP implementation, a peer structure is established for each synchronization source, and these peer structures are stored in a chain in a Hash form. Each peer structure corresponds to a connection.

Figure 4-7 Manycast mode

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Updated: 2019-04-20

Document ID: EDOC1100074722

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